Most important among its changes, I've rewritten the communications code to the LJ server such that it is more reliable - it can even run under a 56K modem without trouble. There's also been improvements made in the Friends List and Custom Friends Groups code. There has been a number of bug fixes made, as well.
MultiLJ is a multi-window client for Windows XP and Vista. Its primary feature is that it uses internal browsers to display journals, rather than relying on one's default browser. It can display as many journals, profiles, and Friends Pages as one wishes, as well as hosting as many Post Editors as one needs. Post History is supported, as well.